It really is very easy, we did it going from the POFQ to the Poly. when you check out just let the baggage handler know that you are going to another resort. Your luggage is transferred during the day, they told me sometime after 1:00.
I do not know what time it got to the next resort because we went to the parks until dinner time. When we checked in at the poly we let them know our luggage was being held and they brought it up to our rooms within a few minutes.
We are staying one night at the POP before going to the POFQ this December. Since the transfer went so smoothly in the summer we decided to stay at the POP instead of an airport hotel for our first night.